Rustproofing process for iron and product thereof



2'' Sept. 15, 1925. 7 1,553,908

L. H. MARSHALL RUST PROOFING PROCESS FOR IRON AND PRODUCT THEREOF Original Filed April 21 1923 TEMPE RI? TURL' FJHRENHE/ 7' 64/5 WWW 4J4? 4M 4 Patented Sept. 15, 1925.

UNITED STATES PATENT OFFICE.

LESLIE H. MARSHALL, 0F MANSFIELD, OHIO, ASSIGNOR TO THE OHIO BRASS COM- PANY, 0F MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY.

RUSTIROOFING PROCESS FOR IRON AND PRODUCT THEREOF.

Continuation of application Serial No. 633,789, filed April 21, 1923. This application filed May 1, 1923. Serial No. 636,014.

To all whom it may concern:

Be it known that I, LESLIE H. MARSHALL, a citizen of the United States of America, residing at Mansfield, in the county of Richland and State of Ohio, have invented certain new and useful'Improvements in Rustproofing Processes for Iron and Products Thereof, of which the following is a specification.

This invention relates to metallurgy and more particularly it relates to a process of rust proofing malleableized cast iron and the product of that process.

Some of the objects of the invention are to provide a process of galvanizing, sherardizing, or otherwise coating malleable cast iron without impairing the properties of the iron, to provide malleable cast iron so coated and imparting thereto certain new properties and characteristics. Still further objects will appear as the invention is hereinafter disclosed.

This application comprises subject matter disclosed in my co-pending application, Serial Number 633,7 89, filed April 21, 1923, of which this application is a continuation in cart.

1 For many years it has been found that hot galvanizing, sherardizing, or similarly treating malleable cast iron renders a come paratively large portion of a heat, brittle, less ductile, cyrstalline in fracture and low in resistance to shock, while the remainder of the same heat possesses its properties andcharacteristics substantially unnnpared com-.

mercially. In the heretofore unsuccessful efforts to solve the problem of galvanizing, sherardizing or similarly coating malleable cast iron to secure a uniform product of substantially unimpaired characteristics and properties many different theories have been advanced among which are the following: that the composition of the hard iron before malleableizing affects the ultimate product, that the treatment of the iron in the annealing or malleableizing process enters into the problem, that the process of pickling or cleaning the castings, the temperature of the zinc bath, the temperature of the quenching bath, the rate of cooling after coating, the dissolving action of the molten zinc, or combinations of these and other steps enter into the problem.

I have discovered that as the temperature of normal malleable cast iron is raised it passes successively through the following ranges or zones of temperature:

(a) A danger zone, i. e., a range of temperature such that if the iron is raised to a temperature within that zone and subsequently cooled, the iron often, though not invariably, becomes brittle and otherwise changes its properties.

(Z1) A neutral point, i. e. a temperature at which the iron, when raised to and at that temperature and then cooled, possesses substantially the same degree of malleablilty or resilience as it possessed before heating, and

(c) A saftey zone i. e., a range of temperature such that if the iron is raised to a temperature within that zone and subsequently cooled, the ma-lleability and other desirable properties of the iron will be maintained or improved.

I take advantage of the discovery which I have made and as set forth above, and employ it as an important part of the process herein disclosed and the resulting product.

As the first step in practicing my invention is to so heat treat the malleableized cast iron as to render it immune against embrittlement when subjected to the process of applying a coating of zinc or other protective material to its surface, and as this step also tends to improve the characteristics and properties of the iron, so that the finished product is superior to that of normal or commercial malleable cast iron which has been subjected merely to the usual processes of applying a protective coating to the same, I will at some length describe the step of heat treatment.

The step of heat treating which I employ in my process differs from the annealing or re-annealing processes of the prior art in various respects among which are the following: When the so called hard iron is annealed to produce malleable properties therein or the annealed iron re-annealed, it is brought to a temperature above that of the carbon-combining or critical temperature of that particular iron, maintained at that temperature for a period depending upon the composition of the iron and the temperature to which it has been raised, and subsequently cooled. In my process of treating malleableized iron, the temperature of the iron is n eye the carbon=combining or- \WW in.

ritisal.fi r9 tareib .temzperatu si is kept below, the. criticaltemperali1Ze....- Again, malleable cast iron which has been annealed or re-annealed, in accordance with the processes of the prior art, is not stable, but when subsequently raised to a temperature within the danger zone, as in case of hot galvanizing or similarly coating, is beyond control of the operator in that he has no assurance that the iron will not become embrittled, and large quantities of malleable iron castings commonly become embrittled whereas others are reliable, though the composition and annealing proc ess are apparently the same in either case. On the other hand, this step of heat treating the iron and the subsequent quenching imparts to the product of my process stability, i. e., it uniformly retains its malleability even when subsequently heated to a temperature within the danger zone as in hot galvanizing or similarly coating the iron.

Explanation of the heat treating step I employ in my novel process may be facilitated by reference to the drawing which indicates graphically the results of actual tests made by me. The curve A is plotted with temperature in degrees Fahrenheit as abscissa and impact values in percentage of original impact value as ordinates. Curve A represents graphically the result of certain tests and observations made in connection with different specimens all from the same piece of commercial normal malleable cast iron. In making these tests I heated different specimens from 392 F. to a corresponding one of a number of different temperatures between 392 F. and 1472 F. held each particular specimen at its higher temperature for three minutes and then quenched in water at 175 F. After quenching, each specimen was tested in an impact machine of the Izod type to determine its resiliency. Such use of an Izod machine is known to those skilled in the art. It consists in measuring the foot pounds required to fracture a notched specimen (notching is standard practice) under test. As to each specimen, I plotted the temperature to which it had been raised as the abscissa and the per centage impact value of that specimen, as determined from the Izod test machine, as the corresponding ordinate. Therefore, the ordinate of each point on the curve A represents to scale, on a basis of 100 as the impact value of normal malleable cast iron before heating, the percentage impact value of a particular one of a number of specimens, all taken from the same piece of commercial malleable cast iron, and which particular specimen has been raised to a temperature indicated by the corresponding abscissa, and then subsequently treated by quenching as above described.

It will be observed that as the treating temperature is increased from 392 F. to substantially 7 00 F. the resulting malleable cast iron shows increasing embrittlement to a point where the resistance to breaking is only about 16% of that of the untreated product. From 700 F. to 1020 F. th effect of increasing temperature does not appear to further increase the embrittlement, but at approximately 1020 F, the curve suddenly rises, crossing the 100% line which I have termed the normal line, at a temperature of 1103 F. and reaching a point where at a temperature of 1130 F. the resistance under impact to breaking is approximately 154% of the untreated product, thus indicating that if the normal or commercial malleable cast iron represented by curve A is subj ected to a. heat treatment of approximately 1130 F., and then quenched, the impact value is raised above that of the untreated iron, or to be exact, the product will withstand a 54% greater impact blow than the untreated product before it will break and is therefore more resilient. By increasing the temperature above 1130 F. and up to substantially 1t00 F. (the critical temperature at which the free carbon in this iron begins to recombine) the resistance toimpact is lowered slightly from that at 1130 F., and the curve further shows by its sudden drop that a heat treatment above 1400 F. will cause a decrease in the resiliency as shown by the decrease in the impact value.

The malleable cast iron upon which the tests shown by curve A in Fig. 1 are based, contained Per cent. Total carbon 2.10 Silicon .80 Phosphorus .20 Manganese .26 Sulphur .073

Inspection of curve A will indicate that the danger zone of the particular malleable cast iron there graphically shown lies below 1103 F. and that the safety zone thereof lies between 1103 F. and 1400 F. lhe neutral point or temperature marks the: dividing point between the danger and safety zones and this neutral point is indicated by the intersection of the curve with the 100% line, the abscissa of the intersection being 1108 F. It will be noted that the curve A is quite steep at its intersection with the 100% line and rises rapidly to a peak at about 1130 F. In other words, if the particular iron is raised to a temperature of about 1103 F. and then quenched its impact value will be the same as when untreated, but when raised to a temperature of about 1130 F. and then quenched the impact value is increased substantially 54%. In view of these facts and the difficulty of close temperature control or regulation, it is preferable to raise the temperature of the iron to at least 1130 F. and better still1200 F. and then quench, to insure that the impact value of the product shall be no less than 100%, and to secure an otherwise desirable product.

Tests thus far made by me indicate that the time rate of temperature increase in bringing the iron up to the treatment temperature is of relatively minor importance.

Limited tests made to date seem to indicate that the rate of cooling from the heat treatment temperature has an effect upon the impact value or resiliency of the heat treated iron, in that quenching in the air tends to give a product of a higher impact value than quenching in hot water or oil and when allowed to cool with the heating furnace an even higher impact value is secured as shown by the following table which shows the results secured upon the same malleable cast iron used in the tests represented by the curve A in Fig. 1.

Time at 1255 F. Method of quenching. 2

Per cent. 3 minutes Cooled with furnace 181 3 minutes In air 140 3 minutes In hot water--175 F. 133 Same iron untreated. 100

- 0 Impact 'Ilme at 1200 F. Quenched. vahm Per cent. 300 minutes In water175 F 125 50 minutes. In water-175 F 156 3 minutes In water-475 F. 133 Same iron untreated 100 Bearing in mind that hot galvanizing of malleable cast iron is accomplished in a zinc bath at a temperature not less than the melting point of the zinc employed (ap proximately 787 F.) and not to exceed approximately 900 F., it will now be appreciate-d, in view of my discovery above set forth, that such hot galvanizing is carried on well within the danger zone of the malleable cast iron (see curve A), i. e., the zone of temperature at which the worst embrittlemen't commonly occurs. And this fact is borne out by experience in the practical art of hot galvanizing malleable iron castings. The same condition is found with respect to malleable cast iron which is sherardized as in this process the iron is heated to a temperature from 650 F. to 710 F. (approximate) and in case of baked japan the iron may also be embrittled, depending upon the temperature used.

A further and very important feature of this heat treating step resides in the fact that after malleableized cast iron is heated to cause its temperature to pass through and beyond the danger zone and into the safety zone, and then further treated as above described by quenching, it retains the resiliency or impact value and other desirable characteristics and properties imparted to it by such treatment even when subsequently heated to carry it into the danger zone and on the danger zone side of the neutral point or ten'iperatur-e. Thus I found, after treating specimens of malleable cast iron as set forth in connection with curve A (including the step of elevating the temperature of the iron into the safety zone) and subsequently reheating the iron to 84 and quenching in water at 175 F., that the reheating after the heat treatment did not decrease the impact value. In other words the benefits secured by the heat treatment at 1200 F., or other temperature within the safety zone including the step of quenching, remain fixed.

The step of heat treating which I employ in my invention can be carried out by placing the commercial malleable cast iron castings to be heat treated in a furnace having a source of heat to bring them up to the temperature required preferably within the safety zone, and allowing them toremain at the desired temperature for a period of time and sufiicient to insure that the temperature is uniform throughout the material treated which may be found to give the best results and then quenched by cooling with the furnace, or removed from the furnace and quenched in air, water, etc. as may be found to give the desired results, or a continuous type of furnace may be used and the cast ings run out and quenched in air, water or oil at such temperature as desired, and the process made continuous or other means of securing the desired temperature may be used.

I have found that this step of my invention is applicable to malleable cast iron of varying chemical composition, and which has been put through th recognized commercial annealing treatment in the malleableizing process. In this case the novel treatment may be applied to the iron by quenching it after its temperature has been brought below the critical or carbon-combining temperature and before its temperature has dropped below the safety zone of temperature described above.

The next important step in my process is that of applying to the heat treated malleable cast iron the protective coating desired. In the case of a hot galvanized coating of zinc, that is, a coating which adheres to the surface of the iron, the treated articles are cleaned as by sand blast, acid (such as sulphuric, hydrochloric or hydrofluoric), etc., or any of the well known processes for removing the scale, oxide, etc. and then immersed in a bath of molten zinc at a temperature found advisable, which may be from approximately 787 F. to 900 F. After remaining in the bath for a sufiicient time the articles are removed, the surplus zinc shaken therefrom, and the articles quenched in air, water, oil, etc., as may be found desirable.

If the articles are to be given a coating by the sherardizing process, that is, treated with zinc oxid under heat forming a coating of zinc alloyed with the iron on top of which is a coating of zinc as such, the articles after cleaning to remove the scale, etc., are placed in an enclosed drum or receptacle in Contact with zinc dust, or oxidized zinc of preferably to 92% zinc while subjected to heat of from 660 F. to 710 F. (approximate) for several hours as may be found necessary after which the articles are allowed to cool. The heating step in contact with the zinc compound is carried out preferably in a slowly rotating drum.

It will be found that since normal malleable cast iron may be embrittled at a low temperature, that when applying a coating of baked japan to malleable cast iron it will be an advantage to heat treat the articles to a temperature within the safety zone before applying the japan coating and subjecting the articles to a baking heat.

I have not set forth all the variations which may be employed in the step of applying the above protective coatings to the treated iron as the conditions may be varied quite extensively in the steps just described, depending upon the results required, but I have set forth certain conditions which, if employed will permit one skilled in the art to carry out my invention as to process and the product thereof.

Tests I have made upon malleable cast iron of the sam composition and treated the same as that represented by curve A, show that when such iron is heat treated as heretofore described and then subjected to a hot dipped coating of zinc as heretofore described, that the resulting product is not only rendered immune from embrittlement, but its properties and characteristics are improved. Results of such tests are shown graphically in Fig. 1 and are represented by curves X and Y. The specimens were first heat treated to the temperatures within the safety zone and the impact values plotted as ordinates in percent of that of an untreated specimen. The specimens tested were subjected to the temperatures shown for three minutes and then quenched in water at 17 5 F. In curve X the specimens were heat treated, but not galvanized while in curve Y the specimens were first heat treated and subsequently hot galvanized at a temperature of 875 F., as herein described, after heat treating as above described.

Curve X does not coincide exactly with curve A as might be expected since the chemical composition and treatment were the same, but the difference which is small may be accounted for by inherent variations in the method of test. Curve X, however, does correspond in shape to curve A, and curve Y shows that the subsequent application of the zinc coating has changed the physical properties of the iron but little from that represented by curve X.

A specimen of the same iron represented by curves X and Y was hot galvanized at 875 F. but not previously heat treated and the result of the impact test is shown at the point Z which shows that the specimen was embrittled and had only 10% of its normal impact value. The specimens which were heat treated before hot galvanizing showed impact values ranging from 130% to 150% of the normal impact value, depending upon the heat treatment temperature.

In view of the variable conditions met with in commercial malleable cast iron I do not wish to be limited strictly to any specific temperature, time, rate of cooling or other conditions, as different grades or compositions of iron may change the temperature treatments required, and some grades of iron may require different times under the treatment temperature and different rates and means of cooling, nor do I wish to be limited to the composition of the malleable cast iron to which my invention is applicable. I have found, however, that there is a definite range of temperature, for a given grade of malleable cast iron, between the limits of which the iron is embrittled and another range, between the limits of which the iron is improved (see Fig. 1) and rendered immune from embrittlement when again heated at a lower temperature as in galvanizing. Neither do I wish to be limited strictly to any specific conditions relative to the application of the protective coating as the con dit-ions of application of this coating can vary greatly and still secure good results.

I find that treating at a temperature of approximately 1200 F. and then quenching prior to applying the protective coating will, as a rule, secure the desired results, as this temperature falls safely within the heat treatment or safety zone of most grades of commercial malleable castiron.

From the curves shown in Fig. 1 it will be apparent to one skilled in the art that since there are two well defined zones as described, and that heating normal malleable cast iron to a temperature Within the zone which I have specified, as the safety zone and then quenching will protect the iron from embrittlement when reheated to a temperature falling within the danger zone, that one who is producing malleable cast iron or one who is using malleable cast iron can stabilize or protect the same against embrittlement when later reheated by subjecting the iron to a series of tests at different temperatures to determine exactly the limits of the safety and danger zones or by determining the limits of the safety zone of the particular iron and subject the iron to the heat treating step according to the results determined and the method I have disclosed before applying the protective coating.

It is possible to combine the various steps of my invention into a continuous operation by first cleaning the malleableized iron, then bringing the castings up to a temperature, within the safety zone, in a reducing atmosphere so that the surface of the iron will not become oxidized and then plunging the castings into the hot zinc bath without exposing them to the action of an oxidizing atmosphere, then removing the castings from the zinc bath and quenching. The heat treatment can be brought about in a mufile furnace in which the air contacting with the castings is displaced with hydrogen or nitrogen gas, and when the castings have been properly heat treated to automatically plunge them into the zinc bath without exposure to the atmosphere.

It will be appreciated by those skilled in the art that I have disclosed a new and novel process of hot galvanizing, sherardizing or otherwise protecting the surface of malleableized cast iron, by which the properties of the iron are stabilized and rendered immune from embrittlement and also by which the malleability and other desirable properties and characteristics are improved.

One way of practicing my invention is to first subject castings of normal malleable cast iron to a heat treating temperature between the temperature limits of the heat treating or safety zone and then quench and then subject the castings to a process of rendering their surfaces rust proof as above described.

In the appended claims, where I use the word quenched, or quenching, as a step in the process prior to the rust-proofing step or steps, I use such word or words to indi cate air cooling; or liquid cooling; or cooling in a furnace but at a comparatlvely rapid rate such, for example, as would take place in a comparatively small or experimental furnace as distinguished from a large commercial furnace.

I claim:

1. The method of treating malleableized cast iron comprising heating the iron to a temperature well in excess of that used in a hot zinc galvanizing bath, and then quenching the iron to render the iron immune against embrittlement when again heated and then coating the iron by subjecting the iron to a bath of molten.zine.

2. The method of treating malleable cast iron comprising first heating the iron to a temperature which will render the iron immune against embrittlement when later subjected to a lower temperature, and then plunging the iron in a 1nolten batl1 of hot zinc and then removing and quenching the 1I'O11.

3. The method of treating malleableized cast iron comprising heating the iron to a temperature well in excess of that used in a hot zinc galvanizing bath and then quenching the iron to render the iron immune against embrittlement when again heated and then coating the iron by subjecting the iron to a bath of molten zinc.

4. The method of treating malleableized cast iron comprising heating the iron to a temperature of approximately 1200 F., quenching the iron and subjecting the treated iron to a heating process in the presence of zinc or zinc compounds to render the surface of the iron rust proof.

5. The method of treating malleable cast iron comprising subjecting it to a temperature within the limits of the safety zone, then quenching the iron to stabilize its properties when later subjected to a temperature endangering its physical properties and then immersing the iron in a bath of molten zinc to give it a protective coating.

6. The method of treating malleable cast iron which comprises subjecting it to a tem perature Within the limits of the safety zone, then subjecting the iron to a treatment to render the surface resistant to corrosion and then cooling.

7. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature within the limits of its safety zone, then quenching the iron, then subjecting it to a rust proofing process and then cooling.

8. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature in excess of its neutral temperature and below its carbon-combining temperature, quenching the iron and then subjecting the iron to a rust proofing process under heat.

9. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature in excess of its neutral temperature and below its carbon-combining temperature, then coating the iron with zinc by immersing the iron in a bath of molten zinc to render its surface rust proof.

10. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature in excess of its neutral temperature and below its carboncombining temperature, then subjecting the surface of the iron to the action of zinc dust under heat.

11. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature in excess of its neutral temperature and below its carboncombining temperature, then quenching the iron, then alloying zinc with the surface of the iron by subjecting the iron to the action of partially oxidized zinc under heat and then coolin 12. The method of rendering malleableized cast iron rust proof comprising heating the iron to a temperature in excess of its neutral temperature and below its carboncombining temperature, quenching the iron and then subjecting the surface of the iron to the action of zinc under heat.

13. The method of treating malleable cast iron comprising heat treating the iron to a temperature between its neutral and carbon combining temperatures, then quenching, then applying a material to the surface of the iron to render it rust proof and then subjecting to heat.

14. The method of producing rust-proof malleable cast iron which comprises the steps of heating the iron to a temperature above the carbon-combining temperature,

maintaining the iron at that temperature for a period dependent upon the composition of the iron and the temperature to which it has been raised, and cooling the iron'to a iron with a rust-proofing material with the.

application of heat.

16. The method of protecting malleable cast iron against corrosion comprising heating it to a temperature above its neutral temperature and below its carbon-combining temperature, then subjecting the iron to the action of zinc dust containing from 80% to 92% of zinc and simultaneously applying a temperature of 660 F. to 710 F.

In testimony whereof I aflix my signature.

LESLIE H. MARSHALL. 

